Various devices are known for contacting gases with liquids. One such device which has been particularly well suited for diffusing chlorine gas into water is the porous stone diffuser sold by Capital Controls Co., Inc. of Colmar, Pa. In brief, the porous stone diffuser comprises a manifold mounting a check valve and a pair of porous stone pipes extending laterally away from the manifold. When immersed in water, gas flows into the pipes and percolates outwardly through the interstices of the stone particles to mix with the water.
While stone diffuser devices perform well when the gas is chlorine, certain problems have been encountered in those applications where it is desired to contact ammonia with water. In such applications, it has been found that solid reaction products tend to form on the surface of the stone diffuser due to the pH of the solution at the point of contact of the ammonia with the water. The solid reaction products tend to accumulate on the surface of the stone diffuser thereby blocking the gas flow therefrom and requiring periodic removal and replacement.
One known attempt to overcome this problem involves the use of a pipe having a central bore communicating with a pair of lateral passages adjacent one end. A peripheral recess is provided in the pipe inwardly adjacent to the lateral ports. A rubber cap is mounted on the end of the pipe and has a peripheral wall which terminates adjacent to the recess. The flow of gas between the cap and the pipe and into the recess is supposed to provide a self-cleaning function. However, in actual practice it has been found that the reaction product accumulates in the recess, thereby requiring periodic shut-down of the diffuser unit for cleaning.